Showmen's Trade Review (Apr-Jun 1943)

38 SHOWMEN'S TRADE REVIEW May 22, 1943 Know Your Projection Definitions FEED REEL* Reel of film which has not yet passed the aperture. FILM GATE* Movable element which when in operating position, holds the film in proper position against the aperture plate. FIXED RESISTANCE: A resistance having a given, fixed value, as a non-adjustable rheostat. FLAMING OF ARC: In projection a flame emanating from the tips of the electrodes of an electric arc under certain conditions. Its cause may be any one of several things, including impure carbon, carbons working above capacity, high amperage and too great distance between carbon tips. FLICKER.* Occurs when the number of pictures shown on the screen per unit time is not sufficient to insure complete PERSISTENCE OF VISION. FOCAL LENGTH* Distance from the center of a lens to the focal point. FOCAL LENGTH, EQUIVALENT.* Calculated focal length of a combination of lenses or of a thick lens. Equal the focal length of such a simple thin lens as would give an image (of a distant object) the same size as the combination or thick lens gives. FOCAL POINT.* Point at which a lens forms the sharpest image of a very distant object. FOCUS (verb).* To adjust the position of a lens so as to secure the sharpest possible image of an object. FOCUSING SCREW: Thumbscrew by means of which the projection lens is moved forward or backward to focus the image on the screen. FOOT-CANDLE.* Unit of illumination of surface. The average illumination of a surface, measured in foot-candles, equals the LUMINOUS FLUX (expressed in LUMENS) falling on the surface, divided by the area of the surface in square feet. FRAME (noun) : A single photograph on a motion picture film. Third installment of A Practical Glossary of descriptive terms relating to projection. The purpose of this list of definitions is NOT to offer a conventional glossary for reference, but rather certain selected terms that are descriptive more than "scientific" definitions of interest and value only to the technically informed. These terms will prove of interest to managers and other members of the nontechnical theatre staff as a means of better acquaintance with various important items and functions of projection apparatus. (Note (*) appearing after terms indicate such definitions are reprinted with permission from A Selected Glossary for the Motion Picture Technician, Compiled by the Academy Technical Bureau of the Academy of Motion Picture Arts and Sciences.) FRAME (verb) : To so adjust the projector framing device that the film photograph is in correct register over the aperture. FRAME LINE: The line between the top of one image and the bottom of the next in a motion picture film. FRAME LINE NOISE* Noise in reproduction, due to the displacement of the film to the right in the projection machine, so that the beam of light for the sound track shines through part of the picture area as well, and cuts the frame lines. This noise is a type of MOTORBOATING. FRAMING DEVICE * An attachment on the projector which allows the operator to FRAME the picture properly. FROZEN.* Of carbon electrodes, means fused together so that lifting mechanism cannot pull them apart and so strike the arc. FUSE BLOCK : A slap or "block" of insulating material carrying one or more fuses. GENEVA MOVEMENT .* Intermittent movement (produced by a cam-and-star wheel) used in most projection machines. GROUND WIRE: In projection a wire connecting a projector frame with the earth. HOOK-UP.* Diagram of an electrical circuit; or, the construction of such a circuit. HORSE POWER: One horse-power (H.P.) equals 33,000 foot-pounds of work per minute. It is the theoretical amount of work one strong draft horse is supposed to perform if a block and tackle be attached to a weight of 33,000 pounds and the tackle be of such proportion that the horse can, by exerting his full strength, just raise the 33,000 pounds one foot while walking outward pulling on the rope for a period of one minute. Under these conditions one horsepower has been exerted during that minute. That is the theory of the thing. One horse power-hour is the amount of work exerted by one horse during one hour, or by 60 horses during one minute, or by 3,600 horses during one second. In electrics 746 watts is supposed to represent the raising of 33,000 pounds one foot and in one minute, or, in other words, one horse power. IMAGE: In projection optics an image is an image or picture of an object (transparent photograph on film or slide) formed on a receiving surface called a screen, by light rays focused by a lens. IN-AND-OUT MOVEMENT.* That part of the intermittent movement in a motion picture camera which moves the claws in and out of the film perforations. INTERMITTENT MOVEMENT : The mechanism by means of which the intermittent sprocket is operated. INTERMITTENT SPROCKET : The sprocket of a projector by means of which the film is given its intermittent movement at the aperture. KILOWATT: One thousand watts, which equals 1.34 horse-power. KILOWATT HOUR : The use of one kilowatt of electric energy for one hour. KNIFE SWITCH : A switch having a movable blade or blades, usually of copper, which are hinged at one end and make or break contact with parallel spring contact clips at the other. The switch blade takes the place of the conductor between its contact points. LAMBERT.* Unit of brightness. Equals the average brightness of a surface which emits or reflects one lumen per square centimeter of surface. LAMPHOUSE: The metal housing surrounding the light source and carrying mount for the condenser lenses. LEADER: A short length of film attached to the leading title of a subject, or to the beginning of a reel of film, in order to protect it and to allow of threading into the take-up without using the film title for the purpose. LENS : (a) A transparent medium, usually glass, having one or more curved surfaces, for the purpose of changing the direction of rays of light, giving them a direction largely determined by the curvature of the lens surface or surfaces, (b) A combination of single lenses mounted together so as to act as a single (compound) lens. LENS BARREL :* Metal tube in which a lens is mounted. LOAD :* The amount of electric power being drawn from the generators or mains. LOOP : In projection, the slack film left between the upper sprocket and the top of the gate tension shoes and the lower sprocket, in order that the film between the two loops may stop and start intermittently while the rest of the film has continuous motion. LUMEN :* Unit of luminous flux. A source, whose luminous intensity in all directions is one candlepower, emits 4" lumens. MAGAZINE,* Camera or projector camera compartment (necessarily light-tight in a camera) holding the roll of unexposed film; also, the compartment holding the roll of exposed film. FOR YOUR BOOTH EMERGENCY REPAIR PARTS Every National Branch has a stock of emergency repair parts for quick replacement. MAIL ORDER PARTS STOCK National is delivering the genuine Simplex parts exhibitors need, proved by shipments over the past six months greater than ever before. LOAN SERVICE EQUIPMENT Emer gency loan equipment more complete than ever, ready for use when you need it. Today National Theatre Supply provides protection for you on three fronts — a three-way contribution to better projection equipment maintenance. Remember, there has been no rationing of National's eagerness and ability to serve. More than 16 years' experience in serving exhibitors, day or night, is your assurance that National will see you through. NATIONAL THEATRE SUPPLY Division of NATIONAL-. -BlUDWORTH, INC.